Emulsion stability is important to provide long term shelf storage that is needed for commercial emulsions. In the personal care industry, examples of emulsions requiring long-term stability can include certain sunscreens, skin moisturizing formulations, skin creams and hair styling formulations. In these types of personal care formulations, synthetic materials including small molecules have typically been used as emulsifiers. However, certain small molecule emulsifiers may lead to irritation, toxicity, and negative interactions with the cosmetic functional materials in the formulations. In addition, certain small molecule emulsifiers also may not provide the desired long-term emulsion stability.
It is desirable that emulsion stabilizers for personal care compositions be insensitive to salts that may be included in personal care compositions, so that the composition formulator is not unduly constrained in the choice of ingredients to include in a personal care formulation.
Particularly for personal care formulations intended for application to the skin, it is desirable that emulsion stabilizers have tactile qualities that are appealing to the user.
Starches and starch derivatives are known to impart desired tactile qualities to personal care formulations. Starches that are used in such formulations must be at concentrations above about 3%, otherwise the starches can undergo a phenomenon known as retrogradation and precipitate from the formulation.
Cellulose and its derivatives are known to act as emulsifiers, but can impart undesirable tactile qualities when used as emulsifiers in personal care products, particularly for those products intended for application to the skin.
US 2012/0121519 A1, assigned to the common assignee herein, discloses polymeric emulsifiers including polysaccharides modified with one or more cross-linking reagent and with from about 1 mol % to about 10 mol % of one or more ionic reagent, methods for preparing the same, and emulsions including the polymeric emulsifiers.
WO 2009/080657 describes using one or more hydrophobically modified polysaccharide in combination with a fatty acid ester of a polyol to obtain a water-in-oil emulsion that is said to have long-term stability and good sensory properties. The hydrophobically modified polysaccharides described therein include inulins, celluloses and derivatives thereof, starches and agars, and mixtures thereof, and the preferred fatty acid ester of a polyol is polyglyceryl-4 diisostearate/polyhydroxy-stearate/sebacate. As described therein, the oily continuous phase is prepared with the one or more fatty acid ester of a polyol, and the aqueous phase is prepared with the hydrophobically modified polysaccharide, and the two phases are then combined to make a water-in-oil emulsion.
It is one object of the invention to provide emulsion stabilizers that comprise sustainable products, and that provide good long term stability.
It is another object of the invention to provide emulsion stabilizers that provide acceptable tactile qualities when used in personal care formulations.
It is yet another object of the invention to provide emulsion stabilizers that are sufficiently salt-insensitive to facilitate the use of salt compounds in personal care formulations, for example for skin, hair and other personal care applications.